U.S. patent application number 17/601764 was filed with the patent office on 2022-06-30 for non-aqueous electrolyte solution additive for lithium secondary battery, and non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery which include the same.
This patent application is currently assigned to LG Energy Solution, Ltd.. The applicant listed for this patent is LG Energy Solution, Ltd.. Invention is credited to Chul Haeng Lee, Jung Min Lee, Young Min Lim.
Application Number | 20220209294 17/601764 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-30 |
United States Patent
Application |
20220209294 |
Kind Code |
A1 |
Lee; Jung Min ; et
al. |
June 30, 2022 |
Non-Aqueous Electrolyte Solution Additive for Lithium Secondary
Battery, and Non-Aqueous Electrolyte Solution for Lithium Secondary
Battery and Lithium Secondary Battery Which Include the Same
Abstract
An additive for a non-aqueous solution of a lithium secondary
battery, a non-aqueous electrolyte solution including the same, and
a lithium secondary battery include the same are disclosed herein.
In some embodiments, an additive is a compound represented by
Formula 1. The additive may suppress dissolution of transition
metal by forming a stable film on a surface of a positive
electrode. A lithium secondary battery including the non-aqueous
electrolyte solution having the additive has improved swelling and
capacity characteristics at high voltage and during
high-temperature storage because dissolution of metallic impurities
causing failure in the battery is suppressed.
Inventors: |
Lee; Jung Min; (Daejeon,
KR) ; Lim; Young Min; (Daejeon, KR) ; Lee;
Chul Haeng; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Energy Solution, Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG Energy Solution, Ltd.
Seoul
KR
|
Appl. No.: |
17/601764 |
Filed: |
April 16, 2020 |
PCT Filed: |
April 16, 2020 |
PCT NO: |
PCT/KR2020/005115 |
371 Date: |
October 6, 2021 |
International
Class: |
H01M 10/0567 20060101
H01M010/0567; H01M 10/0568 20060101 H01M010/0568; H01M 10/0569
20060101 H01M010/0569; C07F 7/08 20060101 C07F007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2019 |
KR |
10-2019-0045583 |
Claims
1. An additive for a non-aqueous solution of a lithium secondary
battery which is a compound represented by Formula 1: ##STR00005##
wherein, in Formula 1, Y is a substituted or unsubstituted alkylene
group having 1 to 10 carbon atoms.
2. The additive for a lithium secondary battery of claim 1,
wherein, in Formula 1, Y is a substituted or unsubstituted alkylene
group having 2 to 8 carbon atoms.
3. The additive for a lithium secondary battery of claim 1,
wherein, in Formula 1, Y is a substituted or unsubstituted alkylene
group having 4 to 8 carbon atoms.
4. The additive for a lithium secondary battery of claim 1, wherein
the compound represented by Formula 1 comprises at least one
selected from the group consisting of compounds represented by
Formulae 1a to 1c. ##STR00006##
5. A non-aqueous electrolyte solution for a lithium secondary
battery, the non-aqueous electrolyte solution comprising: a lithium
salt; a non-aqueous organic solvent; and the additive of claim
1.
6. The non-aqueous electrolyte solution for a lithium secondary
battery of claim 5, wherein the additive is present in an amount of
0.1 wt % to 9 wt % based on a total weight of the non-aqueous
electrolyte solution.
7. The non-aqueous electrolyte solution for a lithium secondary
battery of claim 5, wherein the additive is present in an amount of
0.5 wt % to 5 wt % based on a total weight of the non-aqueous
electrolyte solution.
8. The non-aqueous electrolyte solution for a lithium secondary
battery of claim 5, wherein the additive is present in an amount of
1 wt % to 5 wt % based on a total weight of the non-aqueous
electrolyte solution.
9. The non-aqueous electrolyte solution for a lithium secondary
battery of claim 5, further comprising a second additive for
forming a solid electrolyte interphase (SEI) which is at least one
selected from the group consisting of a cyclic carbonate-based
compound, a halogen-substituted carbonate-based compound, a
sultone-based compound, a sulfate-based compound, a phosphate-based
compound, a borate-based compound, a nitrile-based compound, a
benzene-based compound, an amine-based compound, a silane-based
compound, and a lithium salt-based compound.
10. A lithium secondary battery comprising the non-aqueous
electrolyte solution of claim 5.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a national phase entry under 35
U.S.C. .sctn. 371 of International Application No.
PCT/KR2020/005115, filed on Apr. 16, 2020, which claims priority
from Korean Patent Application No. 10-2019-0045583, filed on Apr.
18, 2019, the disclosures of which are incorporated by reference
herein.
TECHNICAL FIELD
[0002] The present invention relates to a non-aqueous electrolyte
solution additive for a lithium secondary battery, which may
suppress dissolution of transition metal by forming a stable film
on a surface of a positive electrode, and a non-aqueous electrolyte
solution for a lithium secondary battery and a lithium secondary
battery which include the same.
BACKGROUND ART
[0003] There is a need to develop technology for efficiently
storing and utilizing electrical energy as personal IT devices and
computer networks are developed with the recent development of
information society and the accompanying dependency of society as a
whole on the electrical energy is increased.
[0004] Particularly, studies of electricity storage devices, such
as electric double-layer capacitors and non-aqueous electrolyte
solution secondary batteries represented by lithium ion batteries,
have been extensively conducted as an interest in solving
environmental problems and realizing a sustainable circular society
emerges.
[0005] Among them, since the lithium ion batteries may be
miniaturized to be applicable to a personal IT device and have high
operating voltage and energy density, the lithium ion batteries
have been used in electric vehicles and power storage devices as
well as power sources of notebook computers and mobile phones.
These lithium ion batteries are promising because they have higher
energy density than a lead battery or nickel-cadmium battery and
high capacity may be achieved.
[0006] However, the lithium ion battery has a limitation in that
the capacity of the battery decreases with charge/discharge
cycles.
[0007] Thus, as a method of suppressing the decrease in the
capacity of the battery with charge/discharge cycles, a method of
adding various additives to an electrolyte solution has been
studied.
[0008] The additive forms a film called a solid electrolyte
interphase (SEI) on a surface of an electrode while being
decomposed during initial charge and discharge. Since the SEI is
formed during initial charge/discharge cycles, no electricity is
consumed for the decomposition of a solvent and lithium ions may
travel to and from the electrode through the SEI. That is, the
formation of the SEI may play a large role in improving battery
characteristics, storage characteristics, or load characteristics
by preventing degradation of the electricity storage device, such
as the non-aqueous electrolyte solution secondary battery, when
charge/discharge cycles are repeated.
[0009] A surface structure of a positive electrode collapses due to
a side reaction between a non-aqueous electrolyte solution and the
positive electrode while the film formed on the surface of the
electrode degrades when the battery is operated under high-voltage
and high-temperature conditions, and, as a result, transition metal
ions included in the positive electrode may be dissolved into the
non-aqueous electrolyte solution.
[0010] As described above, in a case in which an amount of metallic
impurities in the battery is increased, the metallic impurities may
be re-deposited on the positive electrode to cause an increase in
resistance of the positive electrode, or, in contrast, may be
transferred to a negative electrode through the electrolyte
solution and then electro-deposited on the negative electrode to
grow as dendrites, and, eventually, it causes an internal
short-circuit of the battery. Also, the metallic impurities are
known as factors to consume lithium ions or increase interfacial
resistance of the negative electrode while promoting an additional
electrolyte solution decomposition reaction by destructing the SEI
that gives passivation ability to the negative electrode.
[0011] Thus, there is a need to develop a non-aqueous electrolyte
solution with a new configuration which may prevent a low-voltage
failure and the resulting degradation of battery lifetime by
suppressing the dissolution of positive electrode transition metals
when the battery is operated under high-voltage and
high-temperature conditions.
PRIOR ART DOCUMENT
[0012] Korean Patent Application Laid-open Publication No.
2017-0018975
DISCLOSURE OF THE INVENTION
Technical Problem
[0013] An aspect of the present invention provides a non-aqueous
electrolyte solution additive for a lithium secondary battery which
may suppress dissolution of transition metal by forming a stable
film on a surface of a positive electrode.
[0014] Another aspect of the present invention provides a
non-aqueous electrolyte solution for a lithium secondary battery
which includes the non-aqueous electrolyte solution additive.
[0015] Another aspect of the present invention provides a lithium
secondary battery including the non-aqueous electrolyte solution
for a lithium secondary battery.
Technical Solution
[0016] According to an aspect of the present invention, there is
provided a non-aqueous electrolyte solution additive for a lithium
secondary battery which is a compound represented by Formula 1:
##STR00001##
[0017] in Formula 1,
[0018] Y is a substituted or unsubstituted alkylene group having 1
to 10 carbon atoms.
[0019] According to another aspect of the present invention, there
is provided a non-aqueous electrolyte solution for a lithium
secondary battery which includes a lithium salt, a non-aqueous
organic solvent, and the non-aqueous electrolyte solution additive
for a lithium secondary battery.
[0020] According to another aspect of the present invention, there
is provided a lithium secondary battery including the non-aqueous
electrolyte solution for a lithium secondary battery.
Advantageous Effects
[0021] A compound represented by Formula 1, which is used as a
non-aqueous electrolyte solution additive for a lithium secondary
battery of the present invention, is a compound containing at least
one cyano group in its structure, wherein, since it may form a
stable film on a surface of a positive electrode to prevent
dissolution of transition metal and suppress a side reaction
between the positive electrode and an electrolyte solution, an
amount of metallic impurities in the battery may be reduced.
[0022] Accordingly, if a non-aqueous electrolyte solution for a
lithium secondary battery including the non-aqueous electrolyte
solution additive for a lithium secondary battery is used, a
lithium secondary battery having improved battery swelling and
capacity characteristics during high-voltage and high-temperature
storage may be achieved.
MODE FOR CARRYING OUT THE INVENTION
[0023] Hereinafter, the present invention will be described in more
detail.
[0024] It will be understood that words or terms used in the
specification and claims shall not be interpreted as the meaning
defined in commonly used dictionaries, and it will be further
understood that the words or terms should be interpreted as having
a meaning that is consistent with their meaning in the context of
the relevant art and the technical idea of the invention, based on
the principle that an inventor may properly define the meaning of
the words or terms to best explain the invention.
[0025] With respect to a lithium ion battery, high-temperature
storage characteristics are improved because a film having
passivation ability is formed on surfaces of a negative electrode
and a positive electrode while a non-aqueous electrolyte solution
is decomposed during initial charge and discharge. However,
capacity may be reduced due to a loss of metallic elements while
dissolution of the transition metal elements occurs in the positive
electrode as the film degrades during high-voltage and
high-temperature storage. Also, transition metal ions thus
dissolved are not only electrodeposited on the negative electrode
reacting in a strong reduction potential range to consume
electrons, but also destruct a solid electrolyte interphase (SEI)
during the electrodeposition. As a result, since the surface of the
negative electrode is exposed to cause an additional electrolyte
decomposition reaction, irreversible capacity may eventually be
increased and capacity of a cell may be continuously reduced.
[0026] Thus, the present invention aims at providing a non-aqueous
electrolyte solution additive, which may reduce an amount of
metallic impurities in the battery by preventing the dissolution of
the transition metals and suppressing a side reaction between the
positive electrode and the electrolyte solution through the
formation of a stable film on the surface of the positive
electrode, and a non-aqueous electrolyte solution including the
same. Also, the present invention aims at providing a lithium
secondary battery in which battery swelling and capacity
characteristics during high-voltage and high-temperature storage
are improved by including the non-aqueous electrolyte solution.
[0027] Non-aqueous Electrolyte Solution Additive for Lithium
Secondary Battery
[0028] First, the present invention aims at providing a non-aqueous
electrolyte solution additive which may form a passivation film
able to protect the surface of the positive electrode at a high
voltage on the surface of the positive electrode and has an
excellent adsorption effect with metallic foreign matter by
containing at least one cyano group.
[0029] That is, in the present specification, provided is a
compound represented by the following Formula 1 as the non-aqueous
electrolyte solution additive for a lithium secondary battery:
##STR00002##
[0030] in Formula 1,
[0031] Y may be a substituted or unsubstituted alkylene group
having 1 to 10 carbon atoms.
[0032] In this case, in Formula 1, Y may be a substituted or
unsubstituted alkylene group having 2 to 8 carbon atoms, and,
specifically, may be a substituted or unsubstituted alkylene group
having 4 to 8 carbon atoms.
[0033] More specifically, the compound represented by Formula 1 may
include at least one selected from the group consisting of
compounds represented by Formulae 1a to 1c below.
##STR00003##
[0034] Since the compound represented by Formula 1 contains at
least one polar cyano group (i.e., --CN, nitrile group) having a
high dipole moment at both ends in its structure, it forms a
complex structure or ligand by forming a stronger bond with the
surface of the positive electrode at high temperatures, and thus,
it may form a stable ion conductive film on the surface of the
positive electrode.
[0035] Particularly, the cyano group has a high tendency to adsorb
to ions of metals, such as cobalt (Co), manganese (Mn), or nickel
(Ni), dissolved from the positive electrode due to a repeated
charge and discharge process of the battery or chemical dissolution
reaction of the electrolyte solution, or adsorb to metallic foreign
matter incorporated from raw materials or during a preparation
process. Thus, with respect to a compound having a structure in
which at least one cyano group is substituted into a silicon
element as in the compound represented by Formula 1, for example, a
structure containing three --CN end groups at each silicon (Si)
atom based on a Si--CN bond that provides a stable chemical bond,
since binding sites and binding energy with metal ions are
increased in comparison to a nitrile-based compound used as a
conventional additive, an effect of suppressing metal dissolution
from the positive electrode, for example, an effect of suppressing
generation of metal ions in the battery is excellent.
[0036] Thus, the compound represented by Formula 1 may suppress
dissolution of metallic foreign matter from the positive electrode
by forming a stable film on the surface of the positive electrode
even if a small amount thereof is used, and, furthermore, may
further improve battery swelling and capacity characteristics
during high-voltage and high-temperature storage by suppressing
generation of gas generated by the side reaction between the
positive electrode and the electrolyte solution.
[0037] Furthermore, in addition to the adsorption of metal ions,
unshared electrons of nitrogen (N) of the cyano group may stabilize
anions of a salt to suppress the generation of HF due to the
decomposition of the salt and to prevent precipitation of a portion
of the dissolved transition metals on the surface of the negative
electrode during high-temperature storage.
[0038] In the compound represented by Formula 1, it is preferable
that a length of chain between the Si atom and the Si atom is 10
carbons or less. That is, in a case in which the chain length is
greater than 10 carbons, there is a disadvantage that the compounds
are agglomerated with each other to reduce solubility in an organic
solvent. Thus, in Formula 1, in a case in which the length of the
chain between the Si atom and the Si atom satisfies 1 to 10
carbons, since electron clouds become larger to increase
electrostatic interaction with metal cations, the binding energy
with the metal ions increases.
[0039] Non-aqueous Electrolyte Solution for Lithium Secondary
Battery
[0040] Also, an embodiment of the present invention may provide a
non-aqueous electrolyte solution for a lithium secondary battery
which includes the non-aqueous electrolyte solution additive of the
present invention, a lithium salt, and a non-aqueous organic
solvent.
[0041] (1) Non-aqueous Electrolyte Solution Additive
[0042] The non-aqueous electrolyte solution of the present
invention includes the above-described compound represented by
Formula 1 as the non-aqueous electrolyte solution additive.
[0043] In this case, since a description of the non-aqueous
electrolyte solution additive overlaps with that described above,
the description thereof will be omitted.
[0044] However, in relation to an amount of the non-aqueous
electrolyte solution additive, the compound represented by Formula
1, as the non-aqueous electrolyte solution additive, may be
included in an amount of 0.1 wt % to 9 wt %, particularly 0.5 wt %
to 5 wt %, and more particularly 1 wt % to 5 wt %, for example, 3
wt % to 5 wt % based on a total weight of the non-aqueous
electrolyte solution for a lithium secondary battery.
[0045] In a case in which the compound represented by Formula 1 is
included in an amount within the above range, a stable film may be
formed on the surfaces of the negative electrode and the positive
electrode, and an excellent metal dissolution suppression effect
may also be achieved to prepare a secondary battery having more
improved overall performance. If the amount of the compound
represented by Formula 1 is less than 0.1 wt %, the metallic
foreign matter in the battery may be removed, but, since it is
difficult to continuously maintain its effect, the metallic foreign
matter removal effect may be reduced over time. Also, if the amount
of the additive is greater than 9 wt %, the metal dissolution
suppression effect is improved, but, since a decrease in ionic
conductivity due to an increase in viscosity of the non-aqueous
electrolyte solution may adversely affect mobility of ions in the
battery, rate capability or low-temperature life characteristics
may be degraded.
[0046] Preferably, if the compound represented by Formula 1 is
included in an amount of 0.5 wt % to 5 wt %, particularly 1 wt % to
5 wt %, and more particularly 3 wt % to 5 wt %, an optimum metal
dissolution suppression effect and an effect of suppressing an
increase in the metallic foreign matter in the battery may be
achieved more effectively while suppressing a decrease in capacity
and an increase in resistance due to the side reaction as much as
possible.
[0047] (2) Lithium Salt
[0048] Any lithium salt typically used in an electrolyte solution
for a lithium secondary battery may be used as the lithium salt
without limitation, and, for example, the lithium salt may include
Li.sup.+ as a cation, and may include at least one selected from
the group consisting of F.sup.-, Cl.sup.-, Br.sup.-, I.sup.-,
NO.sub.3.sup.-, N(CN).sub.2.sup.-, BF.sub.4.sup.-, ClO.sub.4.sup.-,
B.sub.10Cl.sub.10.sup.-, AlCl.sub.4.sup.-, AlO.sub.2.sup.-,
PF.sub.6.sup.-, CF.sub.3SO.sub.3.sup.-, CH.sub.3CO.sub.2.sup.-,
CF.sub.3CO.sub.2.sup.-, AsF.sub.6.sup.-, SbF.sub.6.sup.-,
CH.sub.3SO.sub.3.sup.-, (CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-,
(CF.sub.3SO.sub.2).sub.2N.sup.-, (FSO.sub.2).sub.2N.sup.-,
BF.sub.2C.sub.2O.sub.4.sup.-, BC.sub.4O.sub.8.sup.-,
PF.sub.4C.sub.2O.sub.4.sup.-, PF.sub.2C.sub.4O.sub.8.sup.-,
(CF.sub.3).sub.2PF.sub.4.sup.-, (CF.sub.3).sub.3PF.sub.3.sup.-,
(CF.sub.3).sub.4PF.sub.2.sup.-, (CF.sub.3).sub.5PF.sup.-,
(CF.sub.3).sub.6P.sup.-, C.sub.4F.sub.9SO.sub.3.sup.-,
CF.sub.3CF.sub.2SO.sub.3.sup.-, CF.sub.3CF.sub.2
(CF.sub.3).sub.2CO.sup.-, (CF.sub.3SO.sub.2).sub.2CH.sup.-,
CF.sub.3 (CF.sub.2).sub.7SO.sub.3.sup.-, and SCN.sup.- as an
anion.
[0049] Specifically, the lithium salt may include a single material
selected from the group consisting of LiCl, LiBr, LiI, LiBF.sub.4,
LiClO.sub.4, LiB.sub.10Cl.sub.10, LiAlCl.sub.4, LiAlO.sub.2,
LiPF.sub.6, LiCF.sub.3SO.sub.3, LiCH.sub.3CO.sub.2,
LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6, LiCH.sub.3SO.sub.3,
LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO.sub.2F).sub.2),
LiBETI (lithium bis(perfluoroethanesulfonyl)imide,
LiN(SO.sub.2CF.sub.2CF.sub.3).sub.2), and LiTFSI (lithium
bis(trifluoromethane sulfonyl)imide, LiN(SO.sub.2CF.sub.3).sub.2)
or a mixture of two or more thereof. In addition to them, a lithium
salt typically used in an electrolyte solution for a lithium
secondary battery may be used without limitation.
[0050] The lithium salt may be appropriately changed in a normally
usable range, but may be included in a concentration of 0.8 M to
4.0 M, for example, 1.0 M to 3.0 M in the electrolyte solution to
obtain an optimum effect of forming a film for preventing corrosion
of the surface of the electrode.
[0051] If the concentration of the lithium salt is less than 0.8 M,
an effect of improving low-temperature output and cycle
characteristics during high-temperature storage of the lithium
secondary battery is insignificant, and, if the concentration of
the lithium salt is greater than 4.0 M, electrolyte solution
impregnability may be reduced due to the increase in the viscosity
of the non-aqueous electrolyte solution.
[0052] (3) Non-aqueous Organic Solvent
[0053] The non-aqueous organic solvent may include at least one
organic solvent selected from the group consisting of a cyclic
carbonate-based organic solvent, a linear carbonate-based organic
solvent, a linear ester-based organic solvent, and a cyclic
ester-based organic solvent.
[0054] Specifically, the organic solvent may include a cyclic
carbonate-based organic solvent, a linear carbonate-based organic
solvent, or a mixed organic solvent thereof.
[0055] The cyclic carbonate-based organic solvent is an organic
solvent which may well dissociate the lithium salt in the
electrolyte due to high permittivity as a highly viscous organic
solvent, wherein specific examples of the cyclic carbonate-based
organic solvent may be at least one organic solvent selected from
the group consisting of ethylene carbonate (EC), propylene
carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate,
1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene
carbonate, and, among them, the cyclic carbonate-based organic
solvent may include ethylene carbonate.
[0056] Also, the linear carbonate-based organic solvent is an
organic solvent having low viscosity and low permittivity, wherein
typical examples of the linear carbonate-based organic solvent may
be at least one organic solvent selected from the group consisting
of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl
carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate,
and ethylpropyl carbonate, and the linear carbonate-based organic
solvent may specifically include ethyl methyl carbonate (EMC).
[0057] Furthermore, in order to prepare an electrolyte solution
having high ionic conductivity, the organic solvent may further
include at least one ester-based organic solvent selected from the
group consisting of a linear ester-based organic solvent and a
cyclic ester-based organic solvent in addition to at least one
carbonate-based organic solvent selected from the group consisting
of the cyclic carbonate-based organic solvent and the linear
carbonate-based organic solvent.
[0058] Specific examples of the linear ester-based organic solvent
may be at least one organic solvent selected from the group
consisting of methyl acetate, ethyl acetate, propyl acetate, methyl
propionate, ethyl propionate, propyl propionate, and butyl
propionate.
[0059] Also, the cyclic ester-based organic solvent may include at
least one organic solvent selected from the group consisting of
.gamma.-butyrolactone, .gamma.-valerolactone, .gamma.-caprolactone,
.sigma.-valerolactone, and .epsilon.-caprolactone.
[0060] Any organic solvent typically used in an electrolyte
solution for a lithium secondary battery may be added and used
without limitation as the organic solvent, if necessary. For
example, at least one organic solvent selected from an ether-based
organic solvent, an amide-based organic solvent, and a
nitrile-based organic solvent may be further included.
[0061] (4) Additive for Forming SEI
[0062] Also, the non-aqueous electrolyte solution for a lithium
secondary battery of the present invention may further include
additives for forming a SEI in the non-aqueous electrolyte
solution, if necessary, in order to prevent the occurrence of the
collapse of the negative electrode due to the decomposition of the
non-aqueous electrolyte solution in a high power environment or to
further improve low-temperature high rate discharge
characteristics, high-temperature stability, overcharge prevention,
and an effect of suppressing battery swelling at high
temperature.
[0063] As a representative example, the additive for forming an SEI
may include at least one additive for forming an SEI which is
selected from the group consisting of a cyclic carbonate-based
compound, a halogen-substituted carbonate-based compound, a
sultone-based compound, a sulfate-based compound, a phosphate-based
compound, a borate-based compound, a nitrile-based compound, a
benzene-based compound, an amine-based compound, a silane-based
compound, and a lithium salt-based compound.
[0064] The cyclic carbonate-based compound may include vinylene
carbonate (VC) or vinylethylene carbonate.
[0065] The halogen-substituted carbonate-based compound may include
fluoroethylene carbonate (FEC).
[0066] The sultone-based compound may include at least one compound
selected from the group consisting of 1,3-propane sultone (PS),
1,4-butane sultone, ethane sultone, 1,3-propene sultone (PRS),
1,4-butene sultone, and 1-methyl-1,3-propene sultone.
[0067] The sulfate-based compound may include ethylene sulfate
(Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate
(MTMS).
[0068] The phosphate-based compound may include at least one
compound selected from the group consisting of lithium
difluoro(bisoxalato)phosphate, lithium difluorophosphate,
tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite,
tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl)
phosphite.
[0069] The borate-based compound may include tetraphenylborate and
lithium oxalyldifluoroborate.
[0070] The nitrile-based compound may include at least one compound
selected from the group consisting of succinonitrile, adiponitrile,
acetonitrile, propionitrile, butyronitrile, valeronitrile,
caprylonitrile, heptanenitrile, cyclopentane carbonitrile,
cyclohexane carbonitrile, 2-fluorobenzonitrile,
4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile,
phenylacetonitrile, 2-fluorophenylacetonitrile, and
4-fluorophenylacetonitrile.
[0071] The benzene-based compound may include fluorobenzene, the
amine-based compound may include triethanolamine or ethylene
diamine, and the silane-based compound may include
tetravinylsilane.
[0072] The lithium salt-based compound is a compound different from
the lithium salt included in the non-aqueous electrolyte solution,
wherein the lithium salt-based compound may include at least one
compound selected from the group consisting of LiPO.sub.2F.sub.2,
LiODFB, LiBOB (lithium bis(oxalato)borate
(LiB(C.sub.2O.sub.4).sub.2)), and LiBF.sub.4.
[0073] In a case in which vinylene carbonate, vinylethylene
carbonate, or succinonitrile, among these additives for forming an
SEI, is further included, a more robust SEI may be formed on the
surface of the negative electrode during an initial activation
process of the secondary battery.
[0074] In a case in which the LiBF.sub.4 is included,
high-temperature stability of the secondary battery may be improved
by suppressing the generation of gas which may be generated due to
the decomposition of the electrolyte solution at high
temperature.
[0075] Two or more additives for forming an SEI may be mixed and
used, and the additive for forming an SEI may be included in an
amount of 0.01 wt % to 50 wt %, particularly, 0.01 wt % to 10 wt %,
and preferably 0.05 wt % to 5 wt % based on the total weight of the
electrolyte solution. If the amount of the additive for forming an
SEI is less than 0.01 wt %, an effect of improving low-temperature
output, high-temperature storage characteristics, and
high-temperature life characteristics of the battery is
insignificant, and, if the amount of the additive for forming an
SEI is greater than 50 wt %, the side reaction in the electrolyte
solution may excessively occur during charge and discharge of the
battery. Particularly, if the excessive amount of the additives for
forming an SEI is added, the additives for forming an SEI may not
be sufficiently decomposed at high temperature so that they may be
present in the form of an unreacted material or precipitates in the
electrolyte solution at room temperature. Accordingly, a side
reaction that degrades life or resistance characteristics of the
secondary battery may occur.
[0076] Lithium Secondary Battery
[0077] Also, in another embodiment of the present invention, there
is provided a lithium secondary battery including the non-aqueous
electrolyte solution for a lithium secondary battery of the present
invention.
[0078] After an electrode assembly, in which a positive electrode,
a negative electrode, and a separator between the positive
electrode and the negative electrode are sequentially stacked, is
formed and accommodated in a battery case, the lithium secondary
battery of the present invention may be prepared by injecting the
non-aqueous electrolyte solution of the present invention.
[0079] The positive electrode, the negative electrode, and the
separator, which are included in the lithium secondary battery of
the present invention, may be prepared according to a conventional
method known in the art and used, and are specifically the same as
those described later.
[0080] (1) Positive Electrode
[0081] The positive electrode may be formed by coating a positive
electrode collector with a positive electrode slurry including a
positive electrode active material, a binder, a conductive agent,
and a solvent, and then drying and rolling the coated positive
electrode collector.
[0082] The positive electrode collector is not particularly limited
so long as it has conductivity without causing adverse chemical
changes in the battery, and, for example, stainless steel,
aluminum, nickel, titanium, fired carbon, or aluminum or stainless
steel that is surface-treated with one of carbon, nickel, titanium,
silver, or the like may be used.
[0083] The positive electrode active material is a compound capable
of reversibly intercalating and deintercalating lithium, wherein
the positive electrode active material may specifically include a
lithium composite metal oxide including lithium and at least one
metal such as cobalt, manganese, nickel, or aluminum.
[0084] Specifically, the lithium composite metal oxide may include
lithium-manganese-based oxide (e.g., LiMnO.sub.2,
LiMn.sub.2O.sub.4, etc.), lithium-cobalt-based oxide (e.g.,
LiCoO.sub.2, etc.), lithium-nickel-based oxide (e.g., LiNiO.sub.2,
etc.), lithium-nickel-manganese-based oxide (e.g.,
LiNi.sub.1-YMn.sub.YO.sub.2 (where 0<Y<1),
LiMn.sub.2-ZNi.sub.zO.sub.4 (where 0<Z<2), etc.),
lithium-nickel-cobalt-based oxide (e.g.,
LiNi.sub.1-Y1Co.sub.Y1O.sub.2 (where 0<Y1<1)),
lithium-manganese-cobalt-based oxide (e.g.,
LiCo.sub.1-Y2Mn.sub.Y2O.sub.2 (where 0<Y2<1),
LiMn.sub.2-Z1Co.sub.Z1O.sub.4 (where 0<Z1<2), etc.),
lithium-nickel-manganese-cobalt-based oxide (e.g.,
Li(Ni.sub.pCo.sub.qMn.sub.r1)O.sub.2 (where 0<p<1,
0<q<1, 0<r1<1, and p+q+r1=1) or
Li(Ni.sub.p1Co.sub.q1Mn.sub.r2)O.sub.4 (where 0<p1<2,
0<q1<2, 0<r2<2, and p1+q1+r2=2), etc.), or
lithium-nickel-cobalt-transition metal (M) oxide (e.g.,
Li(Ni.sub.p2Co.sub.q2Mn.sub.r3M.sub.s2)O.sub.2 (where M is selected
from the group consisting of aluminum (Al), iron (Fe), vanadium
(V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg),
and molybdenum (Mo), and p2, q2, r3, and s2 are atomic fractions of
each independent elements, wherein 0<p2<1, 0<q2<1,
0<r3<1, 0<S2<1, and p2+q2+r3+S2=1), etc.), and any one
thereof or a compound of two or more thereof may be included. Among
these materials, in terms of the improvement of capacity
characteristics and stability of the battery, the lithium composite
metal oxide may include LiCoO.sub.2, LiMnO.sub.2, LiNiO.sub.2,
lithium nickel manganese cobalt oxide (e.g.,
Li(Ni.sub.0.6Mn.sub.0.2Co.sub.0.2)O.sub.2,
Li(Ni.sub.0.5Mn.sub.0.3Co.sub.0.2)O.sub.2, or
Li(Ni.sub.0.8Mn.sub.0.1Co.sub.0.1)O.sub.2), Or lithium nickel
cobalt aluminum oxide (e.g.,
LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2, etc.), and, in
consideration of a significant improvement effect due to the
control of types and content ratios of components constituting the
lithium composite metal oxide, the lithium composite metal oxide
may be Li(Ni.sub.0.6Mn.sub.0.2Co.sub.0.2)O.sub.2,
Li(Ni.sub.0.5Mn.sub.0.3Co.sub.0.2)O.sub.2,
Li(Ni.sub.0.7Mn.sub.0.15Co.sub.0.15)O.sub.2, or
Li(Ni.sub.0.8Mn.sub.0.1Co.sub.0.1)O.sub.2, and any one thereof or a
mixture of two or more thereof may be used.
[0085] The positive electrode active material may be included in an
amount of 80 wt % to 99 wt %, for example, 90 wt % to 99 wt %,
based on a total weight of solid content in the positive electrode
slurry. In a case in which the amount of the positive electrode
active material is 80 wt % or less, since energy density is
reduced, capacity may be reduced.
[0086] The binder is a component that assists in the binding
between the active material and the conductive agent and in the
binding with the current collector, wherein the binder is commonly
added in an amount of 1 wt % to 30 wt % based on the total weight
of the solid content in the positive electrode slurry. Examples of
the binder may be polyvinylidene fluoride, polyvinyl alcohol,
carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,
regenerated cellulose, polyvinylpyrrolidone,
polytetrafluoroethylene, polyethylene, polypropylene, an
ethylene-propylene-diene termonomer, a styrene-butadiene rubber, a
fluoro rubber, various copolymers thereof, and the like.
[0087] Also, the conductive agent is a material providing
conductivity without causing adverse chemical changes in the
battery, wherein it may be added in an amount of 1 wt % to 20 wt %
based on the total weight of the solid content in the positive
electrode slurry.
[0088] As a typical example of the conductive agent, a conductive
material, such as: carbon powder such as carbon black, acetylene
black, Ketjen black, channel black, furnace black, lamp black, or
thermal black; graphite powder such as natural graphite with a
well-developed crystal structure, artificial graphite, or graphite;
conductive fibers such as carbon fibers or metal fibers; conductive
powder such as fluorocarbon powder, aluminum powder, and nickel
powder; conductive whiskers such as zinc oxide whiskers and
potassium titanate whiskers; conductive metal oxide such as
titanium oxide; or polyphenylene derivatives, may be used.
[0089] Furthermore, the solvent may include an organic solvent,
such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount
such that desirable viscosity is obtained when the positive
electrode active material as well as optionally the binder and the
conductive agent are included. For example, the solvent may be
included in an amount such that a concentration of the solid
content in the slurry including the positive electrode active
material as well as optionally the binder and the conductive agent
is in a range of 10 wt % to 60 wt %, for example, 20 wt % to 50 wt
%.
[0090] (2) Negative Electrode
[0091] The negative electrode may be prepared by coating a negative
electrode collector with a negative electrode slurry including a
negative electrode active material, a binder, a conductive agent,
and a solvent, and then drying and rolling the coated negative
electrode collector.
[0092] The negative electrode collector generally has a thickness
of 3 .mu.m to 500 .mu.m. The negative electrode collector is not
particularly limited so long as it has high conductivity without
causing adverse chemical changes in the battery, and, for example,
copper, stainless steel, aluminum, nickel, titanium, fired carbon,
copper or stainless steel that is surface-treated with one of
carbon, nickel, titanium, silver, or the like, an aluminum-cadmium
alloy, or the like may be used. Also, similar to the positive
electrode collector, the negative electrode collector may have fine
surface roughness to improve bonding strength with the negative
electrode active material, and the negative electrode collector may
be used in various shapes such as a film, a sheet, a foil, a net, a
porous body, a foam body, a non-woven fabric body, and the
like.
[0093] Furthermore, the negative electrode active material may
include at least one selected from the group consisting of lithium
metal, a carbon material capable of reversibly
intercalating/deintercalating lithium ions, metal or an alloy of
lithium and the metal, a metal composite oxide, a material which
may be doped and undoped with lithium, and a transition metal
oxide.
[0094] As the carbon material capable of reversibly
intercalating/deintercalating lithium ions, a carbon-based negative
electrode active material generally used in a lithium ion secondary
battery may be used without particular limitation, and, as a
typical example, crystalline carbon, amorphous carbon, or both
thereof may be used. Examples of the crystalline carbon may be
graphite such as irregular, planar, flaky, spherical, or fibrous
natural graphite or artificial graphite, and examples of the
amorphous carbon may be soft carbon (low-temperature sintered
carbon) or hard carbon, mesophase pitch carbide, and fired
cokes.
[0095] As the metal or the alloy of lithium and the metal, a metal
selected from the group consisting of copper (Cu), nickel (Ni),
sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium
(Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr),
silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn),
barium (Ba), radium (Ra), germanium (Ge), aluminum (Al), and tin
(Sn), or an alloy of lithium and the metal may be used.
[0096] One selected from the group consisting of PbO, PbO.sub.2,
Pb.sub.2O.sub.3, Pb.sub.3O.sub.4, Sb.sub.2O.sub.3, Sb.sub.2O.sub.4,
Sb.sub.2O.sub.5, GeO, GeO.sub.2, Bi.sub.2O.sub.3, Bi.sub.2O.sub.4,
Bi.sub.2O.sub.5, Li.sub.xFe.sub.2O.sub.3 (0.ltoreq.x.ltoreq.1),
Li.sub.xWO.sub.2 (0.ltoreq.x.ltoreq.1), and
Sn.sub.xMe.sub.1-xMe'.sub.yO.sub.z (Me: manganese (Mn), Fe, Pb, or
Ge; Me': Al, boron (B), phosphorus (P), Si, Groups I, II and III
elements of the periodic table, or halogen; 0<x.ltoreq.1;
1.ltoreq.y.ltoreq.3; 1.ltoreq.z.ltoreq.8) may be used as the metal
composite oxide.
[0097] The material, which may be doped and undoped with lithium,
may include Si, SiO.sub.x (0<x.ltoreq.2), a Si--Y alloy (where Y
is an element selected from the group consisting of alkali metal,
alkaline earth metal, a Group 13 element, a Group 14 element,
transition metal, a rare earth element, and a combination thereof,
and is not Si), Sn, SnO.sub.2, and Sn--Y (where Y is an element
selected from the group consisting of alkali metal, alkaline earth
metal, a Group 13 element, a Group 14 element, transition metal, a
rare earth element, and a combination thereof, and is not Sn), and
a mixture of SiO.sub.2 and at least one thereof may also be used.
The element Y may be selected from the group consisting of Mg, Ca,
Sr, Ba, Ra, scandium (Sc), yttrium (Y), Ti, zirconium (Zr), hafnium
(Hf), rutherfordium (Rf), V, niobium (Nb), Ta, dubnium (db), Cr,
Mo, tungsten (W), seaborgium (Sg), technetium (Tc), rhenium (Re),
bohrium (Bh), Fe, Pb, ruthenium (Ru), osmium (Os), hassium (Hs),
rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), Cu,
silver (Ag), gold (Au), Zn, cadmium (Cd), B, Al, gallium (Ga), Sn,
In, Ge, P, arsenic (As), Sb, bismuth (Bi), sulfur (S), selenium
(Se), tellurium (Te), polonium (Po), and a combination thereof.
[0098] The transition metal oxide may include lithium-containing
titanium composite oxide (LTO), vanadium oxide, and lithium
vanadium oxide.
[0099] The negative electrode active material may be included in an
amount of 80 wt % to 99 wt % based on a total weight of solid
content in the negative electrode slurry.
[0100] The binder is a component that assists in the binding
between the conductive agent, the active material, and the current
collector, wherein the binder is commonly added in an amount of 1
wt % to 30 wt % based on the total weight of the solid content in
the negative electrode slurry. Examples of the binder may be
polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose
(CMC), starch, hydroxypropylcellulose, regenerated cellulose,
polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene,
polypropylene, an ethylene-propylene-diene monomer, a
styrene-butadiene rubber, a fluoro rubber, and various copolymers
thereof.
[0101] The conductive agent is a component for further improving
the conductivity of the negative electrode active material, wherein
the conductive agent may be added in an amount of 1 wt % to 20 wt %
based on the total weight of the solid content in the negative
electrode slurry. Any conductive agent may be used without
particular limitation so long as it has conductivity without
causing adverse chemical changes in the battery, and, for example,
a conductive material, such as: carbon powder such as carbon black,
acetylene black, Ketjen black, channel black, furnace black, lamp
black, or thermal black; graphite powder such as natural graphite
with a well-developed crystal structure, artificial graphite, or
graphite; conductive fibers such as carbon fibers or metal fibers;
conductive powder such as fluorocarbon powder, aluminum powder, and
nickel powder; conductive whiskers such as zinc oxide whiskers and
potassium titanate whiskers; conductive metal oxide such as
titanium oxide; or polyphenylene derivatives, may be used.
[0102] The solvent may include water or an organic solvent, such as
NMP and alcohol, and may be used in an amount such that desirable
viscosity is obtained when the negative electrode active material
as well as optionally the binder and the conductive agent are
included. For example, the solvent may be included in an amount
such that a concentration of the solid content in the negative
electrode slurry including the negative electrode active material
as well as optionally the binder and the conductive agent is in a
range of 50 wt % to 75 wt %, for example, 50 wt % to 65 wt %.
[0103] (3) Separator
[0104] As the separator included in the lithium secondary battery
of the present invention, a typical porous polymer film generally
used, for example, a porous polymer film prepared from a
polyolefin-based polymer, such as an ethylene homopolymer, a
propylene homopolymer, an ethylene/butene copolymer, an
ethylene/hexene copolymer, and an ethylene/methacrylate copolymer,
may be used alone or in a lamination therewith, and a typical
porous nonwoven fabric, for example, a nonwoven fabric formed of
high melting point glass fibers or polyethylene terephthalate
fibers may be used, but the present invention is not limited
thereto.
[0105] A shape of the lithium secondary battery of the present
invention is not particularly limited, but a cylindrical type using
a can, a prismatic type, a pouch type, or a coin type may be
used.
[0106] Hereinafter, the present invention will be described in more
detail according to examples. However, the invention may be
embodied in many different forms and should not be construed as
being limited to the embodiments set forth herein. Rather, these
example embodiments are provided so that this description will be
thorough and complete, and will fully convey the scope of the
present invention to those skilled in the art.
EXAMPLES
Example 1
[0107] (Preparation of Non-aqueous Electrolyte Solution for Lithium
Secondary Battery)
[0108] A non-aqueous electrolyte solution for a lithium secondary
battery was prepared by adding 1 g of the compound represented by
Formula 1a to 99 g of a non-aqueous organic solvent (ethylene
carbonate (EC):propyl propionate (PP)=3:7 volume ratio) in which
1.2 M LiPF.sub.6 was dissolved (see Table 1 below).
[0109] (Lithium Secondary Battery Preparation)
[0110] A positive electrode active material (LiCoO.sub.2), a
conductive agent (carbon black), and a binder (polyvinylidene
fluoride) were added to N-methyl-2-pyrrolidone (NMP) in a weight
ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid
content: 50 wt %). A 12 .mu.m thick aluminum (Al) thin film, as a
positive electrode collector, was coated with the positive
electrode slurry, dried, and then roll-pressed to prepare a
positive electrode.
[0111] A negative electrode active material (graphite), a binder
(SBR-CMC), and a conductive agent (carbon black) were added to
water, as a solvent, in a weight ratio of 95:3.5:1.5 to prepare a
negative electrode slurry (solid content: 60 wt %). A 6 .mu.m thick
copper (Cu) thin film, as a negative electrode collector, was
coated with the negative electrode slurry, dried, and then
roll-pressed to prepare a negative electrode.
[0112] An electrode assembly was prepared by sequentially stacking
the positive electrode, a polyolefin-based porous separator coated
with inorganic particles (Al.sub.2O.sub.3), and the negative
electrode.
[0113] The electrode assembly was accommodated in a pouch-type
battery case, and the non-aqueous electrolyte solution for a
lithium secondary battery was injected thereinto to prepare a
pouch-type lithium secondary battery.
Example 2
[0114] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that the compound represented by
Formula 1b was included instead of the compound represented by
Formula 1a during the preparation of the non-aqueous electrolyte
solution (see Table 1 below). Also, a lithium secondary battery
including the same was prepared.
Example 3
[0115] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that the compound represented by
Formula 1c was included instead of the compound represented by
Formula 1a during the preparation of the non-aqueous electrolyte
solution (see Table 1 below). Also, a lithium secondary battery
including the same was prepared.
Example 4
[0116] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that 5.0 g of the compound
represented by Formula 1a was added to 95 g of an organic solvent
(ethylene carbonate(EC):propyl propionate (PP)=3:7 volume ratio)
during the preparation of the non-aqueous electrolyte solution (see
Table 1 below). Also, a lithium secondary battery including the
same was prepared.
Example 5
[0117] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that 3.0 g of the compound
represented by Formula 1a was added to 97 g of an organic solvent
(ethylene carbonate(EC):propyl propionate (PP)=3:7 volume ratio)
during the preparation of the non-aqueous electrolyte solution (see
Table 1 below). Also, a lithium secondary battery including the
same was prepared.
Example 6
[0118] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that 0.5 g of the compound
represented by Formula 1a was added to 99.5 g of an organic solvent
(ethylene carbonate(EC):propyl propionate (PP)=3:7 volume ratio)
during the preparation of the non-aqueous electrolyte solution (see
Table 1 below). Also, a lithium secondary battery including the
same was prepared.
Example 7
[0119] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that 0.1 g of the compound
represented by Formula 1a was added to 99.9 g of an organic solvent
(ethylene carbonate(EC):propyl propionate (PP)=3:7 volume ratio)
during the preparation of the non-aqueous electrolyte solution (see
Table 1 below). Also, a lithium secondary battery including the
same was prepared.
Example 8
[0120] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that 10 g of the compound represented
by Formula 1a was added to 90 g of an organic solvent (ethylene
carbonate(EC):propyl propionate (PP)=3:7 volume ratio) during the
preparation of the non-aqueous electrolyte solution (see Table 1
below). Also, a lithium secondary battery including the same was
prepared.
Comparative Example 1
[0121] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that a non-aqueous electrolyte
solution additive was not included during the preparation of the
non-aqueous electrolyte solution (see Table 1 below). Also, a
lithium secondary battery including the same was prepared.
Comparative Example 2
[0122] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that succinonitrile was included
instead of the compound represented by Formula 1a during the
preparation of the non-aqueous electrolyte solution (see Table 1
below). Also, a lithium secondary battery including the same was
prepared.
Comparative Example 3
[0123] A non-aqueous electrolyte solution was prepared in the same
manner as in Example 1 except that a nitrile-based compound
represented by the following Formula 2 was included instead of the
compound represented by Formula 1a during the preparation of the
non-aqueous electrolyte solution (see Table 1 below). Also, a
lithium secondary battery including the same was prepared.
##STR00004##
TABLE-US-00001 TABLE 1 Non-aqueous electrolyte Organic solvent
solution additive Amount Amount Sample name Mixing ratio added (g)
Formula added (g) Example 1 EC:PP = 3:7 99 1a 1 volume ratio
Example 2 EC:PP = 3:7 99 1b 1 volume ratio Example 3 EC:PP = 3:7 99
1c 1 volume ratio Example 4 EC:PP = 3:7 95 1a 5 volume ratio
Example 5 EC:PP = 3:7 97 1a 3 volume ratio Example 6 EC:PP = 3:7
99.5 1a 0.5 volume ratio Example 7 EC:PP = 3:7 99.9 1a 0.1 volume
ratio Example 8 EC:PP = 3:7 90 1a 10 volume ratio Comparative EC:PP
= 3:7 100 -- -- Example 1 volume ratio Comparative EC:PP = 3:7 99
Succino- 1 Example 2 volume ratio nitrile Comparative EC:PP = 3:7
99 2 1 Example 3 volume ratio
EXPERIMENTAL EXAMPLES
Experimental Example 1. Evaluation of Thickness Increase Rate after
High-Temperature Storage
[0124] An activation (formation) process was performed at 0.2 C
rate on the lithium secondary batteries prepared in Examples 1 to 6
and the lithium secondary batteries prepared in Comparative
Examples 1 to 3. Thereafter, gas in each battery was removed
through a degassing process, a battery in an initial state was
completed by performing a post-activation process in which each
battery having gas removed therefrom was charged at 0.2 C rate to
4.45 V under a constant current/constant voltage condition at room
temperature (25.degree. C.) cut-off charged at 0.05 C, and then
discharged at 0.2 C rate to 3.0 V. The charge and discharge process
was performed using PNE-0506 charge/discharge equipment
(manufacturer: PNE SOLUTION Co., Ltd.).
[0125] Subsequently, after each lithium secondary battery was
constant current/constant voltage charged at 0.7 C rate to 4.45 V
at room temperature (25.degree. C.) and cut-off charged at 0.05 C
under the same condition, a thickness before high-temperature
storage of each lithium secondary battery was measured with a plate
thickness gauge with a weight of 300 g. In this case, a method of
measuring the thickness is performed in such a manner that each
battery was put on the plate thickness gauge and a value appearing
when the weight of 300 g was put on the battery was checked.
[0126] Subsequently, after the batteries were stored at high
temperature by being left standing in an oven (OF-02GW,
manufacturer: JEIO TECH. CO., LTD.) at 85.degree. C. for 8 hours,
each battery was taken out at room temperature and cooled for 24
hours, a thickness of each battery after high-temperature storage
relative to the thickness of the battery before the
high-temperature storage was then measured, and its absolute value
and results of calculating an increase rate (%) are presented in
Table 2 below.
TABLE-US-00002 TABLE 2 Non-aqueous Thickness Thickness electrolyte
before after solution high-tem- high-tem- Thick- additive perature
perature ness Sample Amount storage storage increase name Formula
added (g) (mm) (mm) rate (%) Example 1 1a 1 3.201 3.517 9.87
Example 2 1b 1 3.191 3.526 10.50 Example 3 1c 1 3.205 3.511 9.55
Example 4 1a 5 3.218 3.509 9.04 Example 5 1a 3 3.209 3.515 9.54
Example 6 1a 0.5 3.203 3.578 11.70 Comparative -- -- 3.195 4.186
31.02 Example 1 Comparative Succino- 1 3.202 3.626 13.24 Example 2
nitrile Comparative 2 1 3.203 3.925 22.54 Example 3
[0127] As illustrated in Table 2, with respect to the secondary
batteries of Examples 1 to 6, it may be understood that thickness
increase rates after high-temperature storage were all excellent,
at 12% or less.
[0128] In contrast, a thickness increase rate after
high-temperature storage of the secondary battery of Comparative
Example 1 including the non-aqueous electrolyte solution without an
additive was 31% or more, wherein it may be understood that the
thickness increase rate after high-temperature storage was
significantly inferior to those of the secondary batteries of
Examples 1 to 6.
[0129] Also, thickness increase rates after high-temperature
storage of the secondary battery of Comparative Example 2, which
included the non-aqueous electrolyte solution containing
succinonitrile as a nitrile-based additive, and the secondary
battery of Comparative Example 3, which included the non-aqueous
electrolyte solution containing the compound represented by Formula
2, were 13.24% and 22.54%, respectively, wherein it may be
understood that the thickness increase rates after high-temperature
storage were inferior to those of the secondary batteries of
Examples 1 to 6.
Experimental Example 2. Evaluation of Capacity after
High-Temperature Storage
[0130] An activation (formation) process was performed at 0.2 C
rate on the lithium secondary batteries prepared in Examples 1 to 6
and the lithium secondary batteries prepared in Comparative
Examples 1 to 3. Thereafter, gas in each battery was removed
through a degassing process, a battery in an initial state was
completed by performing a post-activation process in which each
battery having gas removed therefrom was charged at 0.2 C rate to
4.45 V under a constant current/constant voltage condition at room
temperature (25.degree. C.) cut-off charged at 0.05 C, and then
discharged at 0.2 C rate to 3.0 V. In this case, the charge and
discharge process was performed using PNE-0506 charge/discharge
equipment (manufacturer: PNE SOLUTION Co., Ltd.).
[0131] Subsequently, after each lithium secondary battery was
constant current/constant voltage charged at 0.7 C rate to 4.45 V
at room temperature (25.degree. C.) and cut-off charged at 0.05 C
under the same condition, the batteries were stored at high
temperature by being left standing in an oven (OF-02GW,
manufacturer: JEIO TECH. CO., LTD.) at 85.degree. C. for 8 hours.
Thereafter, after each battery was taken out at room temperature
and cooled for 24 hours, 3 cycles of constant current/constant
voltage charging at 0.7 C rate to 4.45 V, cut-off charging at 0.05
C, and cut-off discharging at 0.2 C rate to 3.0 V were performed
using the charge/discharge equipment, and discharge capacity in the
last 3.sup.rd cycle was measured. The discharge capacity obtained
was expressed as a percentage (%) relative to theoretical design
capacity (2210 mAh) of the corresponding cell and listed in Table 3
below.
TABLE-US-00003 TABLE 3 Capacity (mAh) after Capacity Sample name
storage at 85.degree. C. retention (%) Example 1 1975.5 89.4
Example 2 1947.4 88.1 Example 3 1936.2 87.6 Example 4 1859.7 84.1
Example 5 1918.6 86.8 Example 6 1871.9 84.7 Comparative 1628.8 73.7
Example 1 Comparative 1821.8 82.4 Example 2 Comparative 1656.6 75.0
Example 3
[0132] As illustrated in Table 3, with respect to the secondary
batteries of Examples 1 to 6, it may be understood that capacity
retentions after high-temperature storage were all excellent, at
about 84% or more.
[0133] In contrast, capacity retention after high-temperature
storage of the secondary battery of Comparative Example 1 including
the non-aqueous electrolyte solution without an additive was 73.7%,
wherein it may be understood that the capacity retention after
high-temperature storage was significantly inferior to those of the
secondary batteries of Examples 1 to 6.
[0134] Also, capacity retentions after high-temperature storage of
the secondary battery of Comparative Example 2, which included the
non-aqueous electrolyte solution containing succinonitrile as a
nitrile-based additive, and the secondary battery of Comparative
Example 3, which included the non-aqueous electrolyte solution
containing the compound represented by Formula 2, were 82.4% and
75.0%, respectively, wherein it may be understood that the capacity
retentions after high-temperature storage were inferior to those of
the secondary batteries of Examples 1 to 6.
Experimental Example 3. Evaluation of Metal (Co) Dissolution after
High-Temperature Storage
[0135] Each of the lithium secondary batteries prepared in Examples
1 to 8 and the lithium secondary batteries prepared in Comparative
Examples 1 and 3 was charged at 0.7 C rate to 4.4 V under a
constant current/constant voltage condition and cut-off charged at
0.05 C once, and stored in an oven at 85.degree. C. for 8
hours.
[0136] Subsequently, after each of the secondary batteries stored
at high temperature was disassembled and one sheet of the negative
electrode was sampled, each sample was thoroughly washed with a
dimethyl carbonate (DMC) solution, and the negative electrode
active material was then scraped off and subjected to ICP analysis
(ICP-OES (PERKIN-ELMER, OPTIMA 5300DV)). A concentration of cobalt
(Co), which was dissolved from the positive electrode and reduced
and electrodeposited on the negative electrode due to the
degradation of the positive electrode and the side reaction with
the electrolyte solution during high-temperature storage, was
measured by the ICP analysis, and the results thereof are presented
in Table 4 below.
TABLE-US-00004 TABLE 4 Non-aqueous electrolyte solution additive
Sample name Formula Amount added (g) Co (mg/kg) Example 1 1a 1 845
Example 2 1b 1 860 Example 3 1c 1 825 Example 4 1a 5 770 Example 5
1a 3 785 Example 6 1a 0.5 912 Example 7 1a 0.1 1030 Example 8 1a 10
748 Comparative -- -- 1650 Example 1 Comparative 2 1 1340 Example
3
[0137] Referring to Table 4, with respect to the secondary
batteries of Examples 1 to 8, it may be understood that amounts of
Co dissolved after high-temperature storage were low at 1,030 mg/kg
or less.
[0138] In contrast, an amount of Co dissolved after
high-temperature storage of the secondary battery of Comparative
Example 1 including the non-aqueous electrolyte solution without an
additive was 1,650 mg/kg, wherein it may be understood that the
amount of Co dissolved after high-temperature storage was
significantly inferior to those of the secondary batteries of
Examples 1 to 8.
[0139] Also, an amount of Co dissolved after high-temperature
storage of the secondary battery of Comparative Example 3, which
included the non-aqueous electrolyte solution containing the
compound represented by Formula 2, was 1,340 mg/kg, wherein it may
be understood that the amount of Co dissolved after
high-temperature storage was inferior to those of the secondary
batteries of Examples 1 to 8.
[0140] With respect to the secondary battery of Example 7 which
included the non-aqueous electrolyte solution containing a trace
amount of the additive, the amount of Co dissolved after
high-temperature storage was 1,030 mg/kg, wherein the metal
dissolution suppression effect was improved in comparison to those
of Comparative Examples 1 and 3, but it may be understood that the
concentration of metal dissolution was relatively increased in
comparison to those of the secondary batteries of Examples 1 to 6
and 8.
Experimental Example 4. Evaluation of Electrolyte Solution Ionic
Conductivity
[0141] In order to identify physical properties of the non-aqueous
electrolyte solutions, ionic conductivities of the non-aqueous
electrolyte solutions prepared in Examples 1, 4, 5, 6, and 8 were
measured at 25.degree. C. using a 5230 ionic conductivity meter by
METTLER TOLEDO, and the results thereof are presented in Table 5
below.
TABLE-US-00005 TABLE 5 Non-aqueous electrolyte solution additive
Ionic conductivity Sample name Formula Amount added (g) (mS/cm)
Example 1 1a 1 8.14 Example 4 1a 5 7.65 Example 5 1a 3 7.97 Example
6 1a 0.5 8.21 Example 8 1a 10 6.88
[0142] Referring to Table 5, with respect to the non-aqueous
electrolyte solution of Example 8, since the excessive amount of
the additive was used, the viscosity of the non-aqueous electrolyte
solution was increased, and thus, it may be understood that an
ionic conductivity value was reduced in comparison to those of the
non-aqueous electrolyte solutions prepared in Examples 1, 4, 5, and
6.
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